There exists a type of respiratory mask, one referred in US patent application publication No. US 2017/0021123 A1, which includes a support frame, a mask pad, and an air duct. The support frame includes a ring-shaped base portion, an insert portion, a positioning pin, and two wing portions. The insert portion extends rearwardly from an inner edge of the base portion, and defines an air channel. The positioning pin extends rearwardly from a top end of the base portion, and has a hooked end distal from the base portion. The wing portions are respectively disposed at lateral sides of the base portion. The mask pad has a main body, a through hole, and a face pad. The main body has an open end portion abutting separably against the base portion of the support frame and defining an opening for extension of the insert portion of the support frame thereinto, and is clamped separably between the wing portions of the support frame. The through hole is formed in the main body. The positioning pin of the support frame engages removably the through hole such that the main body is fastened releasably on the support frame by the positioning pin and the wing portions. The face pad is mounted on the main body for contacting a face of a user. The air duct is connected to the support frame and communicates with the air channel.
While this prior art allows easy assembling and disassembling between the support frame and the mask pad, the respiratory mask can easily deform, which in turn causes leakage or the air from the air duct.